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Radio communication device

Radio communication device description/claims

The present invention relates to a radio communication device that is used as a terminal of a radio communication system having such a multicell configuration that a plurality of terminals share the same channel with each other, or the like, for example, and is capable of receiving a desired signal by suppressing an interference component transmitted from an interference wave source.

In recent years, the demand for an increase in capacity and an increase in speed of a radio communication shows a great rise, and researches on the method of improving further an effective utilization efficiency of finite frequency resources are done eagerly. As one method of them, the approach for utilizing a spatial domain commands public attention. One of the technologies to utilize a spatial domain is the adaptive array antenna (adaptive antenna). This adaptive antenna can receive strongly a desired signal arriving from the desired direction by adjusting an amplitude and a phase by means of a weighting factor (this weighting factor is referred to as a “weight” hereinafter) by which the received signal is multiplied, and can suppress an interference component signal such as a multipath interference, a co-channel interference, or the like. A channel capacity of the communication system can be improved by such interference suppressing effect.

Also, as another technology utilizing a spatial domain, there is the space division multiplexing (abbreviated as “SDM” hereinafter) technology to transmit different data sequences to the same terminal through the physical channel with the same symbol at the same time and the same frequency by utilizing a spatial orthogonality on the channel. The SDM technology is given as an information disclosure in Non-Patent Literature 1, for example. The SDM transmission can be implemented in a propagation environment in which a correlation of the received signal between the antennas is low, by providing a plurality of antenna elements to both a transmitter and a receiver. In this case, the transmitter transmits different data sequences through the physical channel with the same symbol at the same time and the same frequency from plural antennas every antenna element, while the receiver separates signals received through plural antennas provided to the receiver based on the estimate value of the channel characteristic and receives the signals. As a result, an increase in speed of the transmission can be attained by using a plurality of SDM channels without a multilevel modulation. In the case where the SDM transmission is carried out, when the transmitter and the receiver are equipped with antennas in the same number, an increase of channel capacity that is proportional to the number of antennas can be achieved in an environment in which a large number of diffusion bodies exist between the transmitter and the receiver in sufficient S/N (signal to noise ratio) condition.

Non-Patent Literature 1: G. J. Forschini, “Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas”, Bell Labs Tech. J., pp. 41-59, autumn 1996

In the interference suppression in the above adaptive array antenna and the above SDM technology, the spatial filtering process for multiplying the signals that are received by a plurality of antenna elements by the antenna weight and then synthesizing resultant signals to sum up them is applied. For example, the interference suppression operates in compliance with the MMSE (Minimum Mean Square Error) algorithm that maximizes SIR (Signal to Interference power Ratio), or the like. However, as the precondition of such interference suppressing approach, it is supposed that the interference signal as well as the desired signal should be present steadily. For this reason, particularly in the radio communication system such as the wireless LAN or the like using the packet transmission, the interference signal caused by the own cell and other cells appear and disappear like a burst, and the above precondition is not satisfied in some cases. In other words, the above spatial filtering process has such a problem that, when the interference signal is varied after the algorithm of the spatial filtering process was applied, such process cannot effectively achieve the interference suppression.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a radio communication device capable of implementing a spatial filtering adaptable for an interference wave that appears unsteadily and also increasing an interference canceling ability even in a condition that the interference wave does not steadily exist.

A radio communication device of the present invention, includes an interference signal receiving section for receiving an interference signal containing an interference wave component by using an interference wave receiving antenna weight for receiving selectively a signal of the interference wave component; an interference wave level detecting section for detecting a signal level of the interference wave component from an output of the interference signal receiving section; and a signal separating section for changing a desired wave separating/receiving antenna weight used to receive a desired signal, based on the output of the interference signal receiving section.

According to this configuration, the desired wave separating/receiving antenna weight is changed based on the signal level of the interference wave component. Therefore, even in a condition that the interference wave does not steadily exist, a spatial filtering adaptable for an interference wave that appears unsteadily can be implemented and also an interference canceling ability can be increased.

Also, in the radio communication device of the present invention, the desired wave separating/receiving antenna weight is a weight that minimizes an interference wave received power.

Also, in the radio communication device of the present invention, the desired wave separating/receiving antenna weight is a weight that maximizes a signal to interference power ratio.

Also, in the radio communication device of the present invention, the desired wave separating/receiving antenna weight is a weight that minimizes an interference wave received power for k sub-arrays (k is smaller than N) out of N antennas.

Also, in the radio communication device of the present invention, the signal separating section includes a first weight multiplying portion for multiplying a weight to remove preferentially an interference signal from other station, and a second weight multiplying portion for multiplying an output of the first weight multiplying portion by a spatial multiplexing separating weight to separate a spatial multiplexing stream.

Also, in the radio communication device of the present invention, the signal separating section includes a first weight multiplying portion for multiplying a weight to remove preferentially an interference signal from other station, and a second weight multiplying portion for multiplying an output of the first weight multiplying portion by a maximal ratio combining weight to maximize a signal power.

Also, in the radio communication device of the present invention, when an output of the interference wave level detecting section exceeds a predetermined value, the signal separating section receives a desired signal and changes the desired wave separating/receiving antenna weight used to suppress the detected interference wave.

According to this configuration, when a signal level of the interference wave component exceeds a predetermined value, the desired wave separating/receiving antenna weight can be changed to the weight to suppress the interference wave component in excess of the predetermined value. Therefore, the desired wave can be received while suppressing sufficiently the interference wave even in a condition that the interference wave appears unsteadily.

Also, in the radio communication device of the present invention, the interference wave level detecting section detects a signal level of interference wave components from a plurality of interference sources.

According to this configuration, it is possible to detect the signal level of the interference wave components from a plurality of interference sources, prepare the interference wave receiving antenna weight with respect to a plurality of interference waves, change the desired wave separating/receiving antenna weight based on the detected level of a plurality of interference waves, and the like. Therefore, the interference wave that appears unsteadily can be suppressed sufficiently.

Also, in the radio communication device of the present invention, when the signal level of the interference wave components from the plurality of interference sources in an output of the interference wave level detecting section exceeds a predetermined value, the signal separating section receives the desired signal and changes the desired wave separating/receiving antenna weight in response to the signal level of the interference wave components to suppress a plurality of detected interference waves.

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